If you're old-fashioned, you can send a letter to:
Martin Andersson
Departamento de Matemática Aplicada
Universidade Federal Fluminense
Campus do Gragoatá, Bloco G
Rua Professor Marcos Waldemar de Freitas Reis, S/Nº
CEP: 24210-201
São Domingos – Niterói – RJ
Brazil
Phew, that's a long address!
Or you can just write me an e-mail. Simply write nilsmartin, then that funny "a" character with a circle around it, and finish with id.uff.br.